CALIBRATION
Calibration introduction
The GEM5000 gas analyser is carefully calibrated at manufacture and when returned for service. However, it is
sometimes desirable to be able to carry out a calibration process between services.
This section outlines the correct procedures to enable the site engineer to field calibrate the gas analyser.
CH4, CO2 and O2 can be measured by GEM5000 gas analyser as standard; these channels can be user calibrated.
The analysers have other gas channel options that are specified at manufacture; these too can be calibrated.
This section will describe in detail how to calibrate the three standard gas channels plus the CO channel.
For the other gas channel options contact Geotech for advice.
Two important terms that are used within this section are ‘Zero’ and ‘Span’.
Zero: The point at which the gas analyser is calibrated when there is none of the target gases present.
Span: The point at which the gas analyser is calibrated when a known quantity of the target gas is present.
Frequency of calibration – best practice
The GEM5000 gas analysers can be checked against a known concentration of gas, to give confidence that the
analyser is operating as expected at the time and conditions in which it is being used.
It is recommended that the instrument is regularly serviced and calibrated by Geotech in accordance with the
due date on the instrument.
When defining the frequency of user calibration, the following are factors to be considered:
The frequency of use of the analyser (daily?/monthly?).
The level of confidence and accuracy required for readings to be taken.
Historical user calibration data.
Site specific requirements or conditions.
Historical understanding of expected readings on site.
Zeroing of the gas analyser should be undertaken at the start of each day’s monitoring.
Use historical data to drive your frequency of calibration.
If there is no historical data a good starting point for a daily monitoring round is performing a span calibration
once every week or every other week.
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